LTE (Long Term Evolution) technology has two duplex modes, namely FDD (Frequency Division Duplex) and TDD (Time Division Duplex). The FDD mode is to make the uplink transmission and downlink reception of a UE (User Equipment) performed in different frequency bands, namely uplink frequency band and downlink frequency band, and the uplink transmission and the downlink reception can occur at the same time. The TDD mode is that the uplink transmission and downlink reception of a UE are performed at different times, and the uplink transmission and the downlink reception cannot occur simultaneously at a time. The LTE spectrum resources are mainly 2500 MHz˜2690 MHz, wherein 2500 MHz˜2570 MHz is the LTE FDD uplink frequency band, 2620 MHz˜2690 MHz is the LTE FDD downlink frequency band, 2570 MHz˜2620 MHz is the LTE TDD frequency band, and since the LTE technology has two duplex modes of FDD and TDD, from the duplex mode point of view, the LTE network may be divided into two kinds: a FDD kind and TDD kind, and the LTE FDD system network works in the FDD frequency band, and the TDD system network works in the TDD frequency band.
There are two frame structures corresponding to the above two duplex modes. FIG. 1 is a schematic diagram of a frame structure in the LTE/LTE-A FDD system in the related art, as shown in FIG. 1, a 10 millisecond (ms) radio frame is made up of 20 0.5 ms time slots numbered 0˜19, and the time slots 2i and 2i+1 consist into a 1 ms subframe.
FIG. 2 is a schematic diagram of a frame structure in the LTE/LTE-A TDD system in the related art, and as shown in FIG. 2, a 10 ms radio frame consists of two 5 ms half frames, and one half frame comprises five 1 ms subframes, and the subframe i is defined as two 0.5 ms time slots 2i and 2i+1. The uplink and downlink configurations supported in the TDD system are shown in Table 1.
TABLE 1Uplink -Uplink -downlinkdownlinkconfig-switchingSubframe numberurationpoint cycle012345678905 msDSUUUDSUUU15 msDSUUDDSUUD25 msDSUDDDSUDD310 ms DSUUUDDDDD410 ms DSUUDDDDDD510 ms DSUDDDDDDD65 msDSUUUDSUUD
Wherein, for each subframe in a radio frame, “D” indicates a subframe dedicated to the downlink transmission, and “U” indicates a subframe dedicated to the uplink transmission, “S” indicates a special subframe, and it comprises three parts: a Downlink Pilot Time Slot (referred to as DwPTS), a guard interval (referred to as GP) and an uplink pilot time slot (referred to as UpPTS).
The TDD supports 5 ms and 10 ms uplink and downlink switching cycles. If the downlink to uplink switching point cycle is 5 ms, the special subframe will exist in two half frames; if the downlink to uplink switching point cycle is 10 ms, the special subframe only exists in the first half frame. The subframe 0, the subframe 5 and the DwPTS are always used for the downlink transmission. The UpPTS and the subframe following the special subframe are dedicated to the uplink transmission.
In the LTE system, a hybrid automatic repeat request (HARQ) process refers to: when a transmitting end has data to transmit, the receiving end allocates information such as the frequency domain resources and version information required for transmission to the transmitting end through a downlink signaling. The transmitting end sends data according to this information, and stores the data in its own cache at the same time so as to facilitate retransmitting the data. When the receiving end receives the data, it checks, and if the data are received correctly, an acknowledgment (ACK) is sent to the transmitting end. After receiving the ACK, the transmitting end empties the cache memory used in this transmission, and ends this transmission. If the data are not received correctly, a Negative-acknowledgement (NACK) is sent to the transmitting end, and the packets not correctly received are stored in the cache memory of the receiving end, the transmitting end extracts, after receiving the NACK message, the data from its own cache memory and uses a specific version format to retransmit the data on the corresponding subframe and at the corresponding frequency domain location. After the receiving end receives the retransmitted version, the retransmitted version is combined with the previously not correctly received version, and then the combined version is checked again, and then the abovementioned process is repeated until the data are correctly received or the number of transmissions exceeds the threshold of the maximum number of transmissions. The abovementioned ACK or NACK message is collectively referred to as HARQ-ACK message.
In the LTE TDD system, the scheduling timing of a physical downlink shared channel (PDSCH) in the downlink HARQ has the following specification, that is, the scheduling of the downlink HARQ is specified as follows: the UE detecting the PDCCH on the subframe n, and solves the PDSCH of the current subframe according to the PDCCH information.
In the LTE TDD system, the HARQ-ACK message of the PDSCH transmitted in the downlink HARQ has the following timing specification, that is, the downlink HARQ timing relationship is specified as follows: when the UE detects the PDSCH transmission or the PDCCH indicating the downlink SPS release on the subframe n-k, the UE will transmit the corresponding HARQ-ACK message on the uplink subframe n, wherein k belongs to K, and the values of K in different uplink and downlink configurations are shown in Table 2:
TABLE 2Uplink-downlinkconfig-Subframe number nuration01234567890——6—4——6—41——7, 64———7, 64—2——8, 7, 4,————8, 7,——64, 63——7, 6, 116, 55, 4—————4——12, 8, 7,6, 5,——————114, 75——13, 12, 9,———————8, 7, 5,4, 11, 66——775——77—
Compared to the LTE system, the most notable feature of the LTE-A system is that, the LTE-A system introduced the carrier aggregation technology, that is, the bandwidths of the LTE system are aggregated to obtain a greater bandwidth. In a system introduced with the carrier aggregation, a carrier participating the aggregation is called a component carrier (referred to as CC), also referred to as a serving cell. Meanwhile, the concepts of primary component carrier/serving cell (referred to as PCC/PCell) and secondary component carrier/serving cell (referred to as SCC/SCell) are also proposed. A carrier-aggregated system comprises at least one primary serving cell and one secondary serving cell, wherein the primary serving cell is always in the activated state.
In a wireless communication system, due to the existence of out of band power leakiness, spurious emission and other factors, mutual interference always tend to be produced between the communication devices, in particular when the operating frequency bands only have a small or no frequency band interval. In order to avoid out of band power leakiness, spurious emission and other factors from affecting the communication quality, usually a guard band is set between the working frequency bands, so that there is enough available bandwidth between the system working frequency bands. For example, the FDD and TDD frequency bands in the LTE technology are adjacent, and are likely to interfere with each other in the same coverage, if a guard band of 20 MHz or greater is set between the FDD UL and the TDD, as well as between the TDD DL and the TDD, the interference problem can be solved. However, the spectrum resource is a scarce resource and expensive, and relatively low spectrum resource utilization will result in a waste for resources and economy.
2.6 GHz is the primary LTE frequency band deployed by countries, the FDD&TDD hybrid scheme is the mainstream-planning scheme, and the adjacent channel coexistence is the primary problem to be solved. European research on the Guard band based FDD/TDD LTE@2.6 GHz system coexistence scheme will cause a huge waste of spectrum resources if determining to use the GB, which is very negative for the TDD development and international promotion.
The European FDD operators have both the FDD and TDD frequency bands at the same time, and hope to fully use the FDD and TDD frequency bands to obtain higher transmission rate. Chinese TDD operators require the European TDD frequency band to serve the TDD terminals.
In this regard, using the carrier aggregation technology to aggregate the FDD spectrum and the TDD spectrum is a promising technology. When the FDD and the TDD aggregate, and the TDD works as the primary serving cell while the FDD as the secondary serving cell, the first question needing to be faced is how to determine the timing relationship of the uplink and downlink HARQ. If the FDD serving cell participating in the aggregation is also considered as a special TDD serving cell, that is, the FDD downlink frequency band works as the TDD frequency band with a full downlink configuration, while the FDD uplink frequency band works as the TDD frequency band with a full uplink configuration, in this case, the aggregation of the TDD and the FDD can be seen as the aggregation of TDD serving cells having different uplink and downlink configurations.
For the aggregation of serving cells having different uplink and downlink configurations, the timing relationship between the PDSCH of each serving cell participating in the aggregation and the corresponding HARQ-ACK message, that is the downlink HARQ timing relationship, currently has the following conclusions:                1, the HARQ-ACK message of the PDSCH of a serving cell participating in the aggregation can only be transmitted in the primary uplink serving cell;        2, the timing relationship between the PDSCH of the primary serving cell and the corresponding HARQ-ACK message keeps unchanged.        
When the TDD and the FDD aggregate and the TDD works as the primary serving cell, for the TDD working as the primary serving cell, the timing relationship between its PDSCH and the corresponding HARQ-ACK message keeps unchanged. However, for a FDD serving cell working as a special TDD serving cell, its corresponding uplink and downlink configuration does not exist, nor does its corresponding downlink PDSCH HARQ timing.